Carrier aggregation, CA, features were introduced in Release 10 of the 3GPP standard for Long Term Evolution, LTE, and additional CA features are included in Release 11. CA is also specified for High Speed Packet Access or HSPA. According to CA, a wireless device is configured with a Primary Component Carrier, PCC, and one or more Secondary Component Carriers, SCCs. The network serves the wireless device from a Primary Cell, PCell, on the PCC, and may serve the wireless device from one or more Secondary Cells, SCells, on the one or more SCCs. Note that a configured SCell can be activated and deactivated, and, of course, the particular cell(s) that are included in the carrier aggregation configuration of the wireless device may be changed, e.g., responsive to changing signal conditions, mobility events, etc.
Activation and deactivation of SCells changes the aggregated carrier bandwidth “seen” by the wireless device. Thus, SCell activations and deactivations cause the wireless device to reconfigure its receiver bandwidth responsive to such changes. In turn, reconfiguration of the receiver may cause interruptions on at least the PCell, depending on the corresponding SCell measurement cycle, measCycleSCell, and whether Discontinuous Reception, DRX, is used or not. These interruptions degrade the system performance because they increase the chance of missed packets, e.g., missed ACK/NACK signalling. Furthermore, when the wireless device performs positioning measurements, especially on Positioning Reference Signals, PRS, which are transmitted infrequently, the impact of the interruptions on at least PCell severely degrade the positioning measurements. This degradation, in turn, reduces positioning accuracy. Reduced accuracy in this regard is particularly problematic because positioning measurements are used for a number of critical services e.g. emergency calls.
Among its several advantages, CA provides for enhanced peak-rates. For example, it is possible to use multiple 5 MHz carriers in HSPA to enhance the peak-rate within the HSPA network. Similarly in an LTE network, multiple carriers, each up to 20 MHz in bandwidth, can be aggregated in the UL and/or on DL. Each carrier in multi-carrier or carrier aggregation system is generally termed as a component carrier, CC, or sometimes is referred to as a “cell.” One may assume here that the term “component carrier” or “CC” simply means an individual carrier used for carrier aggregation in a multi-carrier wireless communication network. Similarly, the terms “CA” and “carrier aggregation” may be used interchangeably with “multi-carrier system,” “multi-cell operation,” “multi-carrier operation,” and “multi-carrier transmission” and/or “multi-carrier reception.”
CA may be used for transmission of signaling and data in the uplink and downlink directions. As earlier noted, one of the CCs operates as the PCC, which may also be referred to as the “anchor carrier.” Also as noted, the remaining CCs are called SCCs, or “supplementary” carriers. Generally, the PCC carries the essential device-specific signaling and it exists in both uplink and downlink directions. The network may assign different PCCs to different devices operating in the same sector or cell.
Therefore, a user equipment, UE, or other wireless device may have more than one serving cell in the downlink and/or in the uplink. For example, a given wireless device may have one primary serving cell operating on the PCC and one or more serving SCells operating on the SCC. The serving cell is interchangeably called as primary cell, PCell, or primary serving cell, PSC. The PCell and SCell(s) enable the device to receive and/or transmit data. More specifically, the PCell and SCell exist in DL and/or UL for the reception and transmission of data by the device. The remaining non-serving cells on the PCC and SCC are called neighbor cells. That is, there may be one or more neighbor cells operating on the same PCC and one or more neighbor cells operating on the same SCC.
The CCs belonging to the CA may belong to the same frequency band, which is referred to as intra-band CA. Alternatively, the CCs may belong to different frequency bands, which is referred to as inter-band CA. Further, a given CA configuration may include both intra-band and inter-band CCs, e.g., two CCs in band A and one CC in band B. Still further, an inter-band CA configuration that includes carriers distributed over two bands is called dual-band-dual-carrier-HSDPA, DB-DC-HSDPA, in HSPA networks, and is referred to simply as inter-band CA in LTE networks.
Furthermore the CCs in intra-band CA may be adjacent or non-adjacent in the frequency domain. The latter case is referred to as intra-band non-adjacent CA. A hybrid CA configuration that includes intra-band adjacent CCs, intra-band non-adjacent CCs, and inter-band CCs is also possible. Using CA between carriers of different technologies is also referred to as “multi-RAT carrier aggregation” or as “multi-RAT-multi-carrier system” or simply as “inter-RAT carrier aggregation.” In one example of multi-RAT CA, carriers from WCDMA and LTE are aggregated. In another example of multi-RAT CA, carriers from LTE and CDMA2000 are aggregated. For the sake of clarity, the aggregation of carriers of the same RAT may be referred to as “intra-RAT” CA, or simply as “single RAT” CA. Unless noted otherwise, the term “CA” as used herein may refer to any such types of carrier aggregation.
The CCs included in a given CA configuration may or may not be co-located. That is, not all CCs included in a given CA configuration involve the same site, base station or other radio network node, such as a relay node, mobile relay, etc. For instance, the CCs may be transmitted or received at different locations. Examples include CA configurations that involve non co-located transmission points in the network. Examples of non co-located transmission points include geographically separated base stations, Remote Radio Heads, RRHs, and/or Remote Radio Units, RRUs. Well-known examples of such arrangements include not only the use of RRUs and/or RRHs, but also more generally the use of Distributed Antenna Systems, DAS, and Coordinated Multipoint, CoMP, transmission and/or reception arrangements.
The teachings herein apply to such arrangements and have direct applicability to CoMP systems, and it should also be noted that CA may be used in conjunction with multi-antenna transmission. For example, signals on each CC included in a CA configuration may be transmitted by a base station to a wireless device over two or more transmit antennas, or may be received by the base station from a wireless device over two or more receive antennas.
In further details, Release 11 provides for an “additional carrier type” or ACT, which may also be referred to as a “new carrier type” or NCT, where one or more SCells can operate on the ACT. An ACT or NCT is a type of SCC but the cells on an ACT may contain a reduced number of certain signals types, where the reduction is defined in the time and/or frequency domains. For example, a cell on an ACT may contain Cell-specific Reference Symbols, CRS, only in one subframe per five milliseconds. The CRS also may be reduced in the frequency domain, e.g., the CRS appear in the central 25 Resource Blocks, RBs, of the overall OFDM time/frequency grid, even if the cell bandwidth, BW, is larger than 25 RBs.
In contrast, in a “legacy” carrier, the CRS are transmitted in every subframe over the entire carrier bandwidth. Also synchronization signals in an ACT potentially have a reduced density in time, as compared to the legacy carrier, which uses five milliseconds. Further, the synchronization signals in an ACT may be transmitted according to a configurable pattern. Thus, an SCell on an ACT is therefore used for receiving data, whereas important control information is mainly sent on the PCell, which is transmitted on the PCC. The PCC is always a normal legacy carrier, i.e., it contains all common channels and signals defined in Release 8.
CA operation requires multi-carrier setup and release procedures, which enable a multi-carrier network to at least temporarily setup or release the use of an SCell in the downlink and/or uplink by a CA-capable wireless device. SCell setup and release involves two main concepts; namely the configuration and de-configuration of SCell(s), and the activation and deactivation of SCell(s).
Using the LTE context as an example, an eNodeB uses the configuration procedure to configure a CA-capable wireless device with one or more SCells, e.g., a downlink SCell, an uplink SCell, or both. On the other hand, the de-configuration procedure is used by the eNodeB to de-configure or remove one or more already configured SCells in the downlink and/or the uplink. The configuration or de-configuration procedure is also used to change the current multi-carrier configuration, such as for increasing or decreasing the number of SCells in the current CA configuration of the wireless device, or for swapping the existing SCells with new ones. The configuration and de-configuration are done by the eNodeB using Radio Resource Control, RRC, signaling.
Further, the eNodeB in LTE can activate one or more currently deactivated SCells on one or more corresponding SCCs. Conversely, the eNodeB can deactivate one or more SCells that are currently active. Thus, the SCells included in the CA configuration of a given wireless device are configured by eNodeB, which can activate and deactivate individual ones of them. The PCell is always activated, and the configured SCells are initially deactivated upon an SCell addition and after a handover of the wireless device.
SCell activation and deactivation is accomplished by sending an Activation/Deactivation Medium Access Control, MAC, control element. The Activation/Deactivation command or more specifically, “Activation/Deactivation MAC control element (CE)” is sent via the MAC layer to the wireless device. This particular MAC CE is identified by a MAC Protocol Data Unit, PDU, subheader having a fixed size and consisting of a single octet—octet 1—containing seven C-fields and one R-field, such as shown in FIG. 1. The Ci and R fields in the Activation/Deactivation MAC control element are defined as follows. For Ci, if there is an SCell configured with SCellIndex i as specified in 3GPP TS 36.331 V10.5.0 (2012-03), this field indicates the activation/deactivation status of the SCell with SCellIndex i. Otherwise, the wireless device shall ignore the Ci field. The Ci field is set to “1” to indicate that the SCell with SCellIndex i shall be activated. The Ci field is set to “0” to indicate that the SCell with SCellIndex i shall be deactivated. The R field is a reserved bit and is set to “0.”
Typically, SCell deactivation is done when there is no data to transmit on the SCell(s). Deactivation enables battery savings at the wireless device. In the current standard, 3GPP TS 36.133, v10.7.0, both uplink and downlink SCells are activated and/or deactivated simultaneously upon receiving the MAC CE. In principle, however, the activation/deactivation can be done independently on uplink and downlink SCells.
As suggested earlier, glitches or interruptions on the PCell can arise with SCell setup or release, including any time an SCell is configured, de-configured, activated or de-activated. Such interruptions primarily occur in cases where the wireless device has a single radio chain to receive and/or transmit more than one CC. For example, in case of intra-band carrier aggregation, where CCs are adjacent, a wireless device may have a single radio that can be reconfigured dynamically for the aggregated BW of 40 MHz, for use of two CCs of 20 MHz BW each.
In particular, the interruptions arise when the wireless device changes its reception and/or transmission bandwidth BW from single-carrier to multiple-carrier operation or vice versa. In order to change the BW, the wireless device has to reconfigure RF components in its RF chain, such as RF filters, power amplifiers, etc. For example, consider a wireless device operating according to a CA configuration in which two downlink carriers are configured, each such carrier having a BW of 20 MHz. It will be understood that one of the CCs operates as the PCC and one of the CCs operates as an SCC. Deactivation of the secondary component carrier by the serving/primary cell causes the wireless device to reduce its transceiver BW e.g. from 40 MHz to 20 MHz. This reconfiguration may cause 5-10 milliseconds of interruption on the PCell, on the PCC. Similarly, if the SCell is configured or de-configured, then the PCell may be interrupted for 15-20 milliseconds.
The setup or release of a downlink SCell may also cause uplink interruptions, such as when the SCell and PCell, or another SCell, are Time Division Duplex, TDD, cells that may have the same or different downlink/uplink subframe configurations, or even when both the SCell and PCell, or another SCell, are Frequency Division Duplex, FDD, cells. Similarly, the setup and release of an uplink SCell may cause interruptions in the downlink, such as when the SCell and PCell, or another SCell, are TDD or FDD cells.
During such interruption periods, the wireless device cannot receive from and/or transmit any signal or information to the network. Furthermore, during such interruptions, the wireless device cannot perform measurements due to its inability to receive and/or transmit signals.
In the current standard, interruptions on the PCell arising from reconfiguration of the receiver bandwidth responsive to SCell activation status changes may be permitted, depending upon the measCycleSCell and whether DRX is used or not. For example, no interruption on the PCell is allowed when no common DRX is used and measCycleSCell<640 milliseconds, or when common DRX is used. On the other hand, interruptions on the PCell of up to 0.5% probability of missed ACK/NACK is permitted when no common DRX is used and when measCycleSCell≧640 milliseconds.
Note that the wireless device may perform measurements on deactivated SCells or other cells on the same SCC as a deactivated SCell. In such cases, the measurements are performed in measurement cycles configured by higher layers. The measurement cycles may have periodicity of 160, 256, 320, or 512 subframes. The maximum time of a measurement within each cycle is currently not restricted by the standard, but in practice it is likely to be up to six subframes in each cycle. As described above, the current standard specifies requirements for interruptions on the PCell when the wireless device performs measurements on an SCC with a deactivated SCell.
Positioning measurements are among the radio signal power, quality and timing or relative timing measurements that a wireless device makes for Radio Resource Management, RRM, and for positioning. Several positioning methods exist for determining the location of a target device, which can be a UE, mobile relay, tablet, laptop computer, PDA, etc. The well-known methods include satellite based methods, such as Assisted General Navigational Satellite System, A-GNSS, measurements. On such example is Assisted Global Positioning System, A-GPS, measurements.
Another approach used in LTE networks relies on Observed Time Difference of Arrival, OTDOA, measurements, which rely on a wireless device making Reference Signal Timing Difference, RSTD, measurements for determining its position. In another approach, a Location Measurement Unit or LMU measures Uplink Time Difference of Arrival, UTDOA, to determine the location of a wireless device. Enhanced cell ID techniques use one or more of device receive/transmit, Rx/Tx, time differences, bases station Rx-Tx time differences, LTE Pilot and/or Reference Signal Received Quality, RSRQ, HSPA CPICH measurements, angle of arrival, AoA, measurements, etc., for determining device position. Further, so called “hybrid” methods combine measurement types or techniques from more than one measurement method, for determining device position.
There are different types of positioning nodes in LTE, such as the Enhanced Serving Mobile Location Center or E-SMLC, or the SUPL Location Platform, SLP, or location server—here “SUPL” denotes “Secure User Plane Location.” In LTE, a positioning node configures a wireless device, eNodeB, or LMU to perform one or more positioning measurements. The positioning measurements are used by the wireless device or the positioning node to determine the device's location. The positioning node communicates with device and eNodeB in LTE using the LTE Positioning Protocol, LPP, or the annex to that protocol, referred to as LPPa.
From a positioning network architecture perspective in LTE, the three key elements include the LCS Client, the LCS target and the LCS Server, where “LCS” denotes Location Services. The LCS Server is a physical or logical entity managing positioning for an LCS target by collecting measurements and other location information, assisting the target in measurements when necessary, and estimating the LCS target location. An LCS Client is a software and/or hardware entity that interacts with an LCS Server for the purpose of obtaining location information for one or more LCS targets, i.e., the entities being positioned. LCS Clients may also reside in the LCS targets themselves. An LCS Client sends a request to the LCS Server to obtain location information, and the LCS Server processes and serves the received requests and sends the positioning results and optionally a velocity estimate to the LCS Client. A positioning request can be originated from the target device or entity, or from a network node or external client.
Position calculations can be conducted, for example, by a positioning server, such as an E-SMLC or SLP in LTE, or may be carried out at least in part in the targeted wireless device. The former approach corresponds to the UE-assisted positioning mode, whilst the latter approach corresponds to the device-based positioning mode, which is referred to as UE-based positioning in 3GPP parlance.
The LPP is a point-to-point protocol between an LCS Server and an LCS target device, and is used for positioning the target device. LPP can be used both in the user and the control plane, and multiple LPP procedures are allowed in series and/or in parallel, thereby reducing latency. LPPa is a protocol between eNodeBs and LCS Servers, and is specified only for control-plane positioning procedures. However, LPPa can be used to assist user-plane positioning, by querying eNodeBs for information and eNodeB measurements. The SUPL protocol is used as a transport for LPP in the user plane. LPP can also be used to convey LPP extension messages inside LPP messages. For example, OMA LPP extensions, LPPe, are being specified to allow for operator-specific assistance data, for example, or to allow for assistance data that cannot be provided with LPP. LPPe also may be useful in supporting additional position reporting formats or new positioning methods.
For uplink positioning, such as UTDOA, LMUs may be used. These LMUs may be standalone, integrated into eNodeBs or co-sited with eNodeBs. In LTE, UTDOA measurements such as uplink, UL, Relative Time of Arrival or UL-RTOA, are performed on Sounding Reference Signals, SRS. To detect an SRS, an LMU needs a number of SRS parameters to generate the SRS sequence that is to be correlated with the UL signals received by the LMU. SRS parameters would have to be provided in the assistance data transmitted by a positioning node to the LMU, where such data may be provided using LMUp. However, the positioning node generally does not know these parameters and must acquire such information from the eNodeB that configured the SRS parameters for the wireless device being positioned. LPPa or a similar protocol could be used to obtain such information.
The OTDOA positioning method relies on the wireless device measuring the timing of downlink signals from multiple eNodeBs. An LCS server provides assistance data to the wireless device, for making the measurements, which are then used to locate the wireless device in relation to the neighboring eNodeBs. In particular, the device measures the timing differences for downlink reference signals received from multiple distinct locations. For each measured neighbor cell, the device measures the RSTD, which is the relative timing difference between the neighbor cell and the reference cell. The UE position estimate is then found as the intersection of hyperbolas corresponding to the measured RSTDs. At least three measurements from geographically dispersed base stations with a good geometry are needed to solve for two coordinates of the terminal and the receiver clock bias. In order to solve for position, precise knowledge of the transmitter locations and transmit timing offset is needed.
The RSTD measurement can be intra-frequency, inter-frequency and/or involve CA. In the case of intra-frequency RSTD, all cells are on the same carrier as that of the serving cell. Inter-frequency RSTD measurements involve measurements on at least one cell that belongs to a frequency/carrier that is different than that of the serving/primary cell. In case of CA, the RSTD is measured on the PCell and/or the SCell, and one or more respective neighbor cells on the same PCC and/or SCC.
With reference to 3GPP TS 36.211, new physical signals dedicated for positioning have been introduced in LTE to facilitate positioning measurements of a proper quality and for a sufficient number of distinct locations. These new signals are referred to as Positioning Reference Signals or PRS, and 3GPP has introduced new low-interference positioning subframes, to further enhance positioning measurements made on the PRS.
PRS are transmitted from one antenna port—port R6—according to a pre-defined pattern that is specified in 3GPP TS 36.211. A frequency shift, which is a function of Physical Cell Identity or PCI, can be applied to the specified PRS patterns, to generate orthogonal patterns and model an effective frequency reuse of six. This arrangement makes it possible to significantly reduce neighbor cell interference on the measured PRS and thus improve positioning measurements. Even though PRS have been specifically designed for positioning measurements and in general are characterized by better signal quality than other reference signals, the standard does not mandate using PRS. Other reference signals, e.g. Cell-specific Reference Symbols or CRS could in principle be used for positioning measurements.
PRS are transmitted in pre-defined positioning subframes grouped by several consecutive subframes. These positioning occasions occur periodically with a certain periodicity of N subframes, i.e. the time interval between two positioning occasions. See FIG. 2 for an example depiction. The standardized periods of N are 160, 320, 640, and 1280 milliseconds, and the number of consecutive subframes may be 1, 2, 4, or 6, as set forth in 3GPP TS 36.211.
Because OTDOA-based positioning requires the measurement of PRS from multiple distinct locations, the wireless device may have to deal with PRS that are much weaker than those it receives from its serving cell. Further, if the wireless device does not have approximate knowledge of when the PRS are expected to arrive in time and the exact PRS pattern used for them, it is obligated to perform signal searching within a large window. Such processing affects the time and accuracy of the measurements, as well as the required device complexity. The earlier mentioned assistance data facilitates positioning measurements made by the wireless device on PRS, by providing it with reference cell information, neighbor cell lists containing the PCIs of neighbor cells, the number of consecutive downlink subframes used for PRS, PRS transmission bandwidth, frequency, etc.
Although PRS and positioning subframes have been standardized for OTDOA-based timing measurements, PRS may be used for other measurements as well. For example, more than just positioning measurements may be performed during positioning subframes. Further, PRS may be measured for purposes other than positioning, such as RSRP and RSRQ measurements. One may refer to PCT/SE2010/051079 for example details and it is noted that in the current standard, RSRP measurements are averaged, without differentiating between measurements made during positioning and non-positioning subframes.
PRS signals can be transmitted with zero power or muted, which should then apply for all PRS resource elements within the same subframe over the entire PRS transmission bandwidth. Muting lowers interference so that OTDOA RSTD measurements can be performed at a lower SINR level. This in turn enables the wireless device to detect and measure a large number of distinct cells or locations, e.g., up to sixteen locations, including the reference cell, according to pre-defined OTDOA RSTD requirements. The particular manner in which PRS are muted has not yet been specified in 3GPP and no signaling is available to notify wireless devices as to whether PRS transmissions in a given cell are to be muted in a certain subframe or not. One possible approach is to have the positioning node send assistance data to the wireless device, where that data indicates muting information for a given cell or cells, e.g. the muting pattern used in a cell.
In regards to measurements, the definitions of currently standardized measurements are found in 3GPP TS 36.214. These measurements are done in LTE for various purposes. For instance, some of these purposes include mobility measurements, which may be referred to as RRM measurements, positioning measurements, Self Organizing Network or SON measurements, Minimization of Drive Tests or MDT measurements, etc. It is typically mandatory for all wireless devices to support all intra-RAT measurements, i.e., inter-frequency and intra-band measurements, and to meet the associated requirements. However, the inter-band and inter-RAT measurements are device capabilities, which are reported to the network during call setup. A device supporting certain inter-RAT measurements should meet the corresponding requirements. For example, a device supporting LTE and WCDMA should also support intra-LTE measurements, intra-WCDMA measurements, and inter-RAT measurements, such as measuring WCDMA when the serving cell is LTE and measuring LTE when the serving cell is WCDMA. Hence, the network can use these capabilities according to some strategy. These capabilities are highly driven by factors such as market demand, cost, typical network deployment scenarios, frequency allocation, etc.
RRM measurements are performed to support RRM, which ensures the efficient use of the available radio resources and provides mechanisms that enable E-UTRAN to meet radio resource related requirements. In particular, RRM in E-UTRAN provides mechanisms for managing radio resources, taking into account single and multi-cell aspects. Example RRM functions include radio bearer control, radio admission control, connection mobility control, dynamic resource allocation and packet scheduling, inter-cell interference coordination, ICIC, certain SON functions related to radio resources, and load balancing. RRM may be intra-RAT and inter-RAT, and the supporting RRM measurements may be intra-frequency, inter-frequency and inter-RAT. Radio nodes and/or the UEs or other wireless devices operating in the E-UTRAN make RRM measurements, and the information may be collected and used by the network in a centralized or distributed manner.
Radio Link Monitoring or RLM represents a particular type of RRM measurement. RLM is based on out-of-sync and in-sync detection of a serving cell. Cell identification reporting represents another type of measurement supporting functions such as E-UTRA cell search, inter-RAT UTRAN cell search, System Information, SI, acquisition, etc. Other RRM measurements include UE transmit power or UE power headroom. The transmit power or power headroom of a device is the difference between the maximum output power of the device and the actual transmit power and is expressed on a log scale. Radio node transmit power, e.g., total or for specific channels or signals, is another type of RRM measurement. Other example measurements include signal strength and signal quality in general, interference and path loss measurements, or timing measurements.
Timing measurements may be performed in support of RRM, positioning, SON, MDT, etc. In LTE, Release 9 standardizes time measurements such as UE Rx-Tx time difference, eNodeB Rx-Tx time difference, Timing Advance or TA, RSTD, UE GNSS Timing of Cell Frames for UE positioning, and E-UTRAN GNSS Timing of Cell Frames for UE positioning. The UE and eNodeB Rx-Tx and TA measurements are similar to round trip time, RTT, measurements used in older network types, and are based on both downlink and uplink transmissions. In particular, for UE Rx-Tx, the device measures the difference between the time of the device's uplink transmission and the received downlink transmission that occurs afterward. For eNodeB Rx-Tx, the eNodeB measures the difference between the time of the eNodeB's downlink transmission and the time of the received uplink transmission that occurs afterward. Additionally, LTE defines timing measurements that are implementation-dependent and are not explicitly standardized, such as one-way propagation delay measurements. eNodeBs, for example, use measurement of one-way propagation delay for estimation of the TA value to signal to a target device.
Inter-frequency measurements in principle may be considered for any positioning method, even though currently not all measurements are specified by the standard as intra- and inter-frequency measurements. Examples of inter-frequency measurements currently specified by the standard are RSTD used for OTDOA, and RSRP and RSRQ, which may be used for functions such as fingerprinting or E-CID. A wireless performs inter-frequency and inter-RAT measurements in measurement gaps. The measurements may be done for various purposes, such as mobility, positioning, SON, MDT, etc. Furthermore, the same gap pattern is used for all types of inter-frequency and inter-RAT measurements. Therefore an E-UTRAN must provide a single measurement gap pattern with constant gap duration for concurrent monitoring, for cell detection and measurements, on all frequency layers and RATs.
In more detail, LTE measurement gaps are configured by the LTE network to enable measurements on the other LTE frequencies and/or other RATs, such as UTRA, GSM, CDMA2000, etc. The gap configuration is signaled to wireless devices operating in the LTE network over RRC protocol, as part of measurement configuration information. A wireless device that requires measurement gaps for OTDOA positioning measurements may send an indication to the network via its serving eNodeB, for example. The network responds to the indication by configuring the measurement. Furthermore, the measurement gaps may need to be configured according to a certain rule. An example rule states that inter-frequency RSTD measurements for OTDOA necessitate that the measurement gaps are configured according to the inter-frequency requirements in 3GPP TS 36.133, Section 8.1.2.6, meaning gap pattern #0 shall be used when inter-frequency RSTD measurements are configured and there should not be measurement gaps overlapping with PRS occasions of cells in the serving frequency.
Inter-RAT measurements are also notable for several reasons. Generally in LTE, inter-RAT measurements are typically defined similarly to inter-frequency measurements. This means that they may also require configuring measurement gaps Examples of inter-RAT measurements specified currently for LTE are UTRA FDD CPICH RSCP, UTRA FDD carrier RSSI, UTRA FDD CPICH Ec/No, GSM carrier RSSI, and CDMA2000 1×RTT Pilot Strength.
For positioning, assuming that LTE FDD and LTE TDD are treated as different RATs, the current standard defines inter-RAT requirements only for FDD-TDD and TDD-FDD measurements, and the requirements are different in the two cases. There are no other inter-RAT measurements specified within any separate RAT for the purpose of positioning and which are possible to report to a positioning node, such as the E-SMLC in LTE. Inter-RAT positioning measurement reporting may be possible with LPPe. However, for devices requiring measurement gaps, the current standard does not allow configuring the measurement gaps for other than inter-frequency RSTD measurements.
Additionally, inter-band measurements refer to the measurement done by a wireless device on a target cell on the carrier frequency belonging to a frequency band that is different than that of the serving cell. Both inter-frequency and inter-RAT measurements can be intra-band or inter-band. Inter-band measurements complement the interest of network operators, where a single network operator owns carriers in different bands and would prefer to make efficient use of carriers by performing load balancing on different carriers. Consider the well-known example of a multi-band GSM terminal capable of operating on 800/900/1800/1900 bands.